Directory UMM :Data Elmu:jurnal:S:Soil Biology And Chemistry:Vol32.Issue11-12.oct2000:
Soil Biology & Biochemistry 32 (2000) 1625±1635
www.elsevier.com/locate/soilbio
Biotic and abiotic factors controlling soil respiration rates in
Picea abies stands
Nina Buchmann*
Max-Planck-Institute for Biogeochemistry, P.O. Box 100164, D-07701 Jena, Germany
Accepted 17 May 2000
Abstract
The response of soil respiration to varying environmental factors was studied in four Picea abies stands (47-, 87-, 111- and
146-year old) during the 1998 growing season. While within-site variations of soil CO2 eux (up to 1.6 mmol CO2 mÿ2 sÿ1) were
larger than their diurnal variability (60%). Trenching shallow ®ne roots during collar insertion and mechanical inhibition
of root in-growth during the following months allowed ®ne root respiration to be separated from microbial respiration only in
times of highest root growth. Microbial respiration seemed to dominate the respiratory CO2 loss from the forest ¯oor (>70%).
The comparison of the annual soil CO2 eux in the 47-year old P. abies stand (about 710 g C mÿ2 yrÿ1) with annual litterfall
and root net primary productivity estimates supported this conclusion. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Microbial respiration; Organic layer; Root respiration; Seasonality; Soil; Respiration; Q10 value
1. Introduction
Soil respiration is a major CO2 ¯ux within terrestrial
ecosystems as well as between the biosphere and the
atmosphere (Schlesinger, 1977; Raich and Schlesinger,
1992; IPCC, 1996). Soil CO2 ¯uxes originate from
autotrophic root respiration and heterotrophic microbial respiration in the rhizosphere and the bulk soil.
Generally, between 50% and 80% of the nocturnal
biosphere±atmosphere CO2 exchange, measured with
* Tel.: +49-3641-64-3721; fax: +49-3641-64-3710.
E-mail address: [email protected] (N. Buchmann).
eddy covariance techniques, are due to soil CO2 eux
(Lavigne et al., 1997). However, during the night,
these measurements of net ecosystem CO2 exchange
are associated with the largest errors (Moncrie et al.,
1997). Thus, detailed information on soil CO2 ¯uxes
and on factors that control these ¯uxes are needed to
constrain the ecosystem carbon budget and to decide
whether or not terrestrial ecosystems are carbon sinks
or sources (Fan et al., 1995; Goulden et al., 1996;
Lavigne et al., 1997; Lindroth et al., 1998). Furthermore, climate and land-use change have the potential
to enhance or reduce soil CO2 ¯uxes. Changes in temperature and precipitation, and also shifts from forest
to agricultural land-use or changing management prac-
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 7 7 - 8
1626
N. Buchmann / Soil Biology & Biochemistry 32 (2000) 1625±1635
tices will aect soil respiration ¯uxes and therefore, the
carbon budget of terrestrial ecosystems (Raich and
Potter, 1995; IPCC, 1996).
Typically, soil CO2 ¯ux rates show large spatial and
temporal variations, both within and among sites,
which are only partly due to methodological dierences (Raich and Nadelhoer, 1989; Hanson et al.,
1993; Norman et al., 1997). Since soil respiration is a
combined ¯ux from roots and microorganisms from
dierent soil depths (organic surface layers and mineral horizons), several factors and their interactions
aect soil respiration rates. Soil temperature and soil
moisture are among the most important factors controlling the CO2 ¯ux (Raich and Schlesinger, 1992;
Raich and Potter, 1995; Davidson et al., 1998). Root
nitrogen concentrations, soil texture, substrate quantity
and quality have also been shown to have an eect
(Grant and Rochette, 1994; Randerson et al., 1996;
Boone et al., 1998; Pregitzer et al., 1998). Great debate
still exists on how to model the impact of these factors
on soil respiration (e.g., Lloyd and Taylor, 1994;
Thierron and Laudelout, 1996), and how the large
variability in¯uences aggregation of soil CO2 eux
estimates for a watershed or a landscape (Kicklighter
et al., 1994). Thus, although the variability of soil CO2
¯uxes and some of the underlying causes are well
known, they still bear uncertainties that need to be
resolved.
Since autotrophic and heterotrophic respiration will
react dierently to changes in environmental conditions, it is crucial to get more insight into both components of soil respiration (Kirschbaum, 1995; Boone
et al., 1998). However, the separation of root (including rhizosphere microorganisms) and microbial respiration under ®eld conditions is still dicult. So far,
many dierent approaches have been used in situ, ranging from severe disturbances of a site to very speci®c
requirements, e.g., changes in the carbon isotopic signature of the two respiratory components (either due
to a change of the photosynthetic pathway of the vegetation or manipulations with isotope tracers). Autotrophic respiration of intact roots has been measured
with root cuvettes in the ®eld (Gansert, 1994) or with
excised roots in the laboratory (Burton et al., 1998).
Trenching (Fisher and Gosz, 1986; Bowden et al.,
1993; Hart and Sollins, 1998; Boone et al., 1998),
labeling with 14C, 13C or 18O (Horwath et al., 1994;
Swinnen et al., 1994; HoÈgberg and Ekblad, 1996; Lin
et al., 1999), inhibiting one respiratory component
with speci®c inhibitors or herbicides (Helal and Sauerbeck, 1991; Nakane et al., 1996), and enhancing one
component over the other (Bowden et al., 1993) have
been used to separate root from microbial respiration.
However, the ratio between the two respiration components is generally quite site-speci®c and varies
between 1:9 and 9:1 (Hanson et al., 2000).
Natural disturbances (e.g., ®re, windthrow) or
anthropogenic land-use changes (e.g., logging, agricultural cultivation, aorestation) often alter the soil pro®le, thereby changing not only carbon stocks, but
maybe also carbon ¯uxes (Schimel et al., 1997). The
magnitude of change in soil CO2 eux is dependent
on whether or not litter and organic layers are
removed, roots are disturbed or mineral soil horizons
are exposed or mixed. However, only very limited information is available about these aspects in forest
ecosystems (Edwards and Sollins, 1973; Bowden et al.,
1993; Mallik and Hu, 1997; Nakane et al., 1997;
Boone et al., 1998; Thuille et al., 2000). Since forest
management always involves some kind of site disturbance, this adds further uncertainty to modeled soil
CO2 ¯ux estimates of managed forests.
In this study, spatial versus temporal variability of
soil respiration was studied in four Picea abies stands
during the 1998 growing season. Spatial variability was
investigated at two dierent scales, within a site and
within a watershed, using stands growing close to each
other (less than 500 m apart). Temporal variability
was addressed on a diurnal and a seasonal basis. Furthermore, the eects of ®ne root exclusion and organic
layer removal on soil CO2 ¯ux rates was tested in Norway spruce forests.
2. Materials and methods
2.1. Sites
Four Norway spruce stands (Picea abies (L.) Karst.)
were chosen within the Lehstenbach watershed, at
about 770 m elevation in the Fichtelgebirge, Northeast
Bavaria, Germany (50808' N, 11852' E). The four
stands were located close to each other (1 mm diameter) within the organic layers were cut with a knife
without disturbing the underlying mineral soil horizons. Soil CO2 eux was determined 24 h later. This
design allowed the organic layer respiration to be separated from mineral soil respiration.
2.4. Statistics
Analyses of variance with a posteriori tests (Tukey's
honestly signi®cant dierence (HSD) test, a 0:05
were used to separate the means. Data were transformed when variances were not homogenous. Nonlinear regression analyses were used to test the eect of
collar establishment. Soil CO2 eux and temperature
data were pooled when the interaction term was not
signi®cant at the a 0:05 level. Correlation and nonlinear regression analyses were used to test the relationship between soil temperature, soil moisture and
soil respiration (Eq. (1)). The Q10 values were calculated according to Eq. (2). Residual analyses were performed to test the exponential regression (Eq. (1))
versus the Lloyd and Taylor (1994) Arrhenius type
equation (Eq. (3)).
y b0 e b1 T
1
Q10 e10b1
2
Table 1
Stand characteristics of four P. abies stands within the Lehstenbach watersheda
Site
Weidenbrunnen
Weidenbrunnen3
Weidenbrunnen2
Coulissenhieb
a
Age (yr)
LAIb
L (cm)
Thickness of Of layer (cm)
Thickness of Oh layer (cm)
47
87
111
146
10.4
NDc
ND
6.6
1.320.3
1.520.1
1.020.1
0.920.1
5.120.4
4.820.7
5.220.6
5.920.2
3.620.8b
4.220.7b
7.220.6a
4.420.2b
Dierent letters within a column denote signi®cantly dierent thickness data (Tukey HSD test, a 0:05).
Leaf area index data provided by Martina Mund, Max-Planck Institute for Biogeochemistry, Jena, Germany.
c
ND Ð not determined.
b
1628
N. Buchmann / Soil Biology & Biochemistry 32 (2000) 1625±1635
where T is the soil temperature (8C).
1
1
ÿ
y R10 exp 308:56
56:02 T ÿ 227:13
3
where R10 is the soil respiration rate at 108C, and T is
the absolute soil temperature (K). See Lloyd and Taylor (1994) for the derivation of the equation.
3. Results
3.1. Spatial versus temporal variability of soil
respiration rates
Within-site spatial variations among soil collars were
larger than the diurnal variability of soil respiration
rates measured with the same collars during a day
(Fig. 1). While within-site dierences of soil CO2 eux
among replicated collars were up to 1.6 mmol CO2 mÿ2
sÿ1 (about 40% of maximum values, between 60%
and 70% of minimum values), diurnal variations were
less than 0.25 mmol CO2 mÿ2 sÿ1 (70%. Similar
results with higher contributions from microbial than
from root respiration were also observed by Kelting et
al. (1998) who separated this microbial component
even further (20% of total soil respiration was due to
microbial respiration in the rhizosphere, 48% were due
to microorganisms in the bulk soil). Killing the root
system after clear-cutting followed by herbicide application (Nakane et al., 1996) as well as using stable carbon and oxygen isotopes to separate the dierent
respiratory ¯uxes (Lin et al., 1999), resulted in microbial respiration rates that were between 50% and
70% of bulk soil respiration. Manipulating litter input,
root presence and soil organic matter contents, Bowden et al. (1993) estimated that only about 33% of
total soil respiration was due to root respiration.
Although all of these dierent experimental
approaches have uncertainties, microbial respiration
(not associated with the rhizosphere) appears to represent the dominant fraction of total soil CO2 eux in
a wide range of terrestrial ecosystems.
Thus, trenching shallow ®ne roots during collar
insertion, subsequent mechanical inhibition of root ingrowth and monitoring soil respiration rates in those
collars over time, is a useful tool to separate root and
microbial respiration in the ®eld. One obvious drawback of this method is the detection of respiration
originating from shallow coarse roots since those can
not be cut with the collars. However, larger trenching
plots of 3 m 3 m (Bowden et al., 1993) resulted in a
very similar distribution of root versus microbial res-
N. Buchmann / Soil Biology & Biochemistry 32 (2000) 1625±1635
piration (33% vs. 67%), supporting the ®ndings with
the small collars (70%). Changes in soil
respiration rates after long-term exclusion of roots can
be the result of several mechanisms. Soil CO2 eux
might be reduced not only because the root component
is lacking, but also because trenching prevents belowground carbon input for microbial decomposition.
Furthermore, soil CO2 ¯ux rates might change due to
a higher soil moisture regime as a result of restricted
plant water uptake (Hart and Sollins, 1998). In this
study, however, soil moisture remained the same, and
during most of the growing season, the duration of
root exclusion did not have an eect on soil CO2 ¯ux
rates, indicating that root respiration in the organic
layer was only a minor component of bulk soil respiration.
The removal of litter and organic layers in this
study generally resulted in a reduction in the soil respiration rates that was less than 40% (Fig. 6). Thus,
the major fraction of the respired CO2 originated not
from organic surface layers, but from mineral horizons, probably the Ah horizon (>60%). Similar
results were reported from a temperate deciduous forest (Edwards and Sollins, 1973) (>60% of total soil
respiration originated from deeper mineral horizons)
and boreal Canadian and Japanese forests (Mallik and
Hu, 1997; Nakane et al., 1997) (between 58% and
74% of the total soil respiration ¯ux originated from
mineral soil horizons). Thus, any natural disturbance
and land-use change that aects the composition of
the soil pro®le will strongly aect soil CO2 eux rates.
According to the results of this and others studies,
such an eect will be larger if mineral soil horizons
were disturbed.
4.4. Annual soil CO2 ¯ux
A comparison of annual soil CO2 eux with annual
litterfall and root net primary productivity estimates
supported the partitioning of total soil respiration in
root and microbial respiratory ¯uxes. The annual soil
CO2 eux for the 47-year old P. abies stand totaled
about 710 g C mÿ2 yrÿ1 (using the exponential
equation given in Table 3 with daily averages of soil
temperatures in the Of layer at 5 cm depth; data provided by C. Rebmann, Max-Planck-Institute for Biogeochemistry, Jena, Germany). Separating this ¯ux
into its microbial and root components resulted in
>500 g C mÿ2 yrÿ1 (>70%) and
www.elsevier.com/locate/soilbio
Biotic and abiotic factors controlling soil respiration rates in
Picea abies stands
Nina Buchmann*
Max-Planck-Institute for Biogeochemistry, P.O. Box 100164, D-07701 Jena, Germany
Accepted 17 May 2000
Abstract
The response of soil respiration to varying environmental factors was studied in four Picea abies stands (47-, 87-, 111- and
146-year old) during the 1998 growing season. While within-site variations of soil CO2 eux (up to 1.6 mmol CO2 mÿ2 sÿ1) were
larger than their diurnal variability (60%). Trenching shallow ®ne roots during collar insertion and mechanical inhibition
of root in-growth during the following months allowed ®ne root respiration to be separated from microbial respiration only in
times of highest root growth. Microbial respiration seemed to dominate the respiratory CO2 loss from the forest ¯oor (>70%).
The comparison of the annual soil CO2 eux in the 47-year old P. abies stand (about 710 g C mÿ2 yrÿ1) with annual litterfall
and root net primary productivity estimates supported this conclusion. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Microbial respiration; Organic layer; Root respiration; Seasonality; Soil; Respiration; Q10 value
1. Introduction
Soil respiration is a major CO2 ¯ux within terrestrial
ecosystems as well as between the biosphere and the
atmosphere (Schlesinger, 1977; Raich and Schlesinger,
1992; IPCC, 1996). Soil CO2 ¯uxes originate from
autotrophic root respiration and heterotrophic microbial respiration in the rhizosphere and the bulk soil.
Generally, between 50% and 80% of the nocturnal
biosphere±atmosphere CO2 exchange, measured with
* Tel.: +49-3641-64-3721; fax: +49-3641-64-3710.
E-mail address: [email protected] (N. Buchmann).
eddy covariance techniques, are due to soil CO2 eux
(Lavigne et al., 1997). However, during the night,
these measurements of net ecosystem CO2 exchange
are associated with the largest errors (Moncrie et al.,
1997). Thus, detailed information on soil CO2 ¯uxes
and on factors that control these ¯uxes are needed to
constrain the ecosystem carbon budget and to decide
whether or not terrestrial ecosystems are carbon sinks
or sources (Fan et al., 1995; Goulden et al., 1996;
Lavigne et al., 1997; Lindroth et al., 1998). Furthermore, climate and land-use change have the potential
to enhance or reduce soil CO2 ¯uxes. Changes in temperature and precipitation, and also shifts from forest
to agricultural land-use or changing management prac-
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 7 7 - 8
1626
N. Buchmann / Soil Biology & Biochemistry 32 (2000) 1625±1635
tices will aect soil respiration ¯uxes and therefore, the
carbon budget of terrestrial ecosystems (Raich and
Potter, 1995; IPCC, 1996).
Typically, soil CO2 ¯ux rates show large spatial and
temporal variations, both within and among sites,
which are only partly due to methodological dierences (Raich and Nadelhoer, 1989; Hanson et al.,
1993; Norman et al., 1997). Since soil respiration is a
combined ¯ux from roots and microorganisms from
dierent soil depths (organic surface layers and mineral horizons), several factors and their interactions
aect soil respiration rates. Soil temperature and soil
moisture are among the most important factors controlling the CO2 ¯ux (Raich and Schlesinger, 1992;
Raich and Potter, 1995; Davidson et al., 1998). Root
nitrogen concentrations, soil texture, substrate quantity
and quality have also been shown to have an eect
(Grant and Rochette, 1994; Randerson et al., 1996;
Boone et al., 1998; Pregitzer et al., 1998). Great debate
still exists on how to model the impact of these factors
on soil respiration (e.g., Lloyd and Taylor, 1994;
Thierron and Laudelout, 1996), and how the large
variability in¯uences aggregation of soil CO2 eux
estimates for a watershed or a landscape (Kicklighter
et al., 1994). Thus, although the variability of soil CO2
¯uxes and some of the underlying causes are well
known, they still bear uncertainties that need to be
resolved.
Since autotrophic and heterotrophic respiration will
react dierently to changes in environmental conditions, it is crucial to get more insight into both components of soil respiration (Kirschbaum, 1995; Boone
et al., 1998). However, the separation of root (including rhizosphere microorganisms) and microbial respiration under ®eld conditions is still dicult. So far,
many dierent approaches have been used in situ, ranging from severe disturbances of a site to very speci®c
requirements, e.g., changes in the carbon isotopic signature of the two respiratory components (either due
to a change of the photosynthetic pathway of the vegetation or manipulations with isotope tracers). Autotrophic respiration of intact roots has been measured
with root cuvettes in the ®eld (Gansert, 1994) or with
excised roots in the laboratory (Burton et al., 1998).
Trenching (Fisher and Gosz, 1986; Bowden et al.,
1993; Hart and Sollins, 1998; Boone et al., 1998),
labeling with 14C, 13C or 18O (Horwath et al., 1994;
Swinnen et al., 1994; HoÈgberg and Ekblad, 1996; Lin
et al., 1999), inhibiting one respiratory component
with speci®c inhibitors or herbicides (Helal and Sauerbeck, 1991; Nakane et al., 1996), and enhancing one
component over the other (Bowden et al., 1993) have
been used to separate root from microbial respiration.
However, the ratio between the two respiration components is generally quite site-speci®c and varies
between 1:9 and 9:1 (Hanson et al., 2000).
Natural disturbances (e.g., ®re, windthrow) or
anthropogenic land-use changes (e.g., logging, agricultural cultivation, aorestation) often alter the soil pro®le, thereby changing not only carbon stocks, but
maybe also carbon ¯uxes (Schimel et al., 1997). The
magnitude of change in soil CO2 eux is dependent
on whether or not litter and organic layers are
removed, roots are disturbed or mineral soil horizons
are exposed or mixed. However, only very limited information is available about these aspects in forest
ecosystems (Edwards and Sollins, 1973; Bowden et al.,
1993; Mallik and Hu, 1997; Nakane et al., 1997;
Boone et al., 1998; Thuille et al., 2000). Since forest
management always involves some kind of site disturbance, this adds further uncertainty to modeled soil
CO2 ¯ux estimates of managed forests.
In this study, spatial versus temporal variability of
soil respiration was studied in four Picea abies stands
during the 1998 growing season. Spatial variability was
investigated at two dierent scales, within a site and
within a watershed, using stands growing close to each
other (less than 500 m apart). Temporal variability
was addressed on a diurnal and a seasonal basis. Furthermore, the eects of ®ne root exclusion and organic
layer removal on soil CO2 ¯ux rates was tested in Norway spruce forests.
2. Materials and methods
2.1. Sites
Four Norway spruce stands (Picea abies (L.) Karst.)
were chosen within the Lehstenbach watershed, at
about 770 m elevation in the Fichtelgebirge, Northeast
Bavaria, Germany (50808' N, 11852' E). The four
stands were located close to each other (1 mm diameter) within the organic layers were cut with a knife
without disturbing the underlying mineral soil horizons. Soil CO2 eux was determined 24 h later. This
design allowed the organic layer respiration to be separated from mineral soil respiration.
2.4. Statistics
Analyses of variance with a posteriori tests (Tukey's
honestly signi®cant dierence (HSD) test, a 0:05
were used to separate the means. Data were transformed when variances were not homogenous. Nonlinear regression analyses were used to test the eect of
collar establishment. Soil CO2 eux and temperature
data were pooled when the interaction term was not
signi®cant at the a 0:05 level. Correlation and nonlinear regression analyses were used to test the relationship between soil temperature, soil moisture and
soil respiration (Eq. (1)). The Q10 values were calculated according to Eq. (2). Residual analyses were performed to test the exponential regression (Eq. (1))
versus the Lloyd and Taylor (1994) Arrhenius type
equation (Eq. (3)).
y b0 e b1 T
1
Q10 e10b1
2
Table 1
Stand characteristics of four P. abies stands within the Lehstenbach watersheda
Site
Weidenbrunnen
Weidenbrunnen3
Weidenbrunnen2
Coulissenhieb
a
Age (yr)
LAIb
L (cm)
Thickness of Of layer (cm)
Thickness of Oh layer (cm)
47
87
111
146
10.4
NDc
ND
6.6
1.320.3
1.520.1
1.020.1
0.920.1
5.120.4
4.820.7
5.220.6
5.920.2
3.620.8b
4.220.7b
7.220.6a
4.420.2b
Dierent letters within a column denote signi®cantly dierent thickness data (Tukey HSD test, a 0:05).
Leaf area index data provided by Martina Mund, Max-Planck Institute for Biogeochemistry, Jena, Germany.
c
ND Ð not determined.
b
1628
N. Buchmann / Soil Biology & Biochemistry 32 (2000) 1625±1635
where T is the soil temperature (8C).
1
1
ÿ
y R10 exp 308:56
56:02 T ÿ 227:13
3
where R10 is the soil respiration rate at 108C, and T is
the absolute soil temperature (K). See Lloyd and Taylor (1994) for the derivation of the equation.
3. Results
3.1. Spatial versus temporal variability of soil
respiration rates
Within-site spatial variations among soil collars were
larger than the diurnal variability of soil respiration
rates measured with the same collars during a day
(Fig. 1). While within-site dierences of soil CO2 eux
among replicated collars were up to 1.6 mmol CO2 mÿ2
sÿ1 (about 40% of maximum values, between 60%
and 70% of minimum values), diurnal variations were
less than 0.25 mmol CO2 mÿ2 sÿ1 (70%. Similar
results with higher contributions from microbial than
from root respiration were also observed by Kelting et
al. (1998) who separated this microbial component
even further (20% of total soil respiration was due to
microbial respiration in the rhizosphere, 48% were due
to microorganisms in the bulk soil). Killing the root
system after clear-cutting followed by herbicide application (Nakane et al., 1996) as well as using stable carbon and oxygen isotopes to separate the dierent
respiratory ¯uxes (Lin et al., 1999), resulted in microbial respiration rates that were between 50% and
70% of bulk soil respiration. Manipulating litter input,
root presence and soil organic matter contents, Bowden et al. (1993) estimated that only about 33% of
total soil respiration was due to root respiration.
Although all of these dierent experimental
approaches have uncertainties, microbial respiration
(not associated with the rhizosphere) appears to represent the dominant fraction of total soil CO2 eux in
a wide range of terrestrial ecosystems.
Thus, trenching shallow ®ne roots during collar
insertion, subsequent mechanical inhibition of root ingrowth and monitoring soil respiration rates in those
collars over time, is a useful tool to separate root and
microbial respiration in the ®eld. One obvious drawback of this method is the detection of respiration
originating from shallow coarse roots since those can
not be cut with the collars. However, larger trenching
plots of 3 m 3 m (Bowden et al., 1993) resulted in a
very similar distribution of root versus microbial res-
N. Buchmann / Soil Biology & Biochemistry 32 (2000) 1625±1635
piration (33% vs. 67%), supporting the ®ndings with
the small collars (70%). Changes in soil
respiration rates after long-term exclusion of roots can
be the result of several mechanisms. Soil CO2 eux
might be reduced not only because the root component
is lacking, but also because trenching prevents belowground carbon input for microbial decomposition.
Furthermore, soil CO2 ¯ux rates might change due to
a higher soil moisture regime as a result of restricted
plant water uptake (Hart and Sollins, 1998). In this
study, however, soil moisture remained the same, and
during most of the growing season, the duration of
root exclusion did not have an eect on soil CO2 ¯ux
rates, indicating that root respiration in the organic
layer was only a minor component of bulk soil respiration.
The removal of litter and organic layers in this
study generally resulted in a reduction in the soil respiration rates that was less than 40% (Fig. 6). Thus,
the major fraction of the respired CO2 originated not
from organic surface layers, but from mineral horizons, probably the Ah horizon (>60%). Similar
results were reported from a temperate deciduous forest (Edwards and Sollins, 1973) (>60% of total soil
respiration originated from deeper mineral horizons)
and boreal Canadian and Japanese forests (Mallik and
Hu, 1997; Nakane et al., 1997) (between 58% and
74% of the total soil respiration ¯ux originated from
mineral soil horizons). Thus, any natural disturbance
and land-use change that aects the composition of
the soil pro®le will strongly aect soil CO2 eux rates.
According to the results of this and others studies,
such an eect will be larger if mineral soil horizons
were disturbed.
4.4. Annual soil CO2 ¯ux
A comparison of annual soil CO2 eux with annual
litterfall and root net primary productivity estimates
supported the partitioning of total soil respiration in
root and microbial respiratory ¯uxes. The annual soil
CO2 eux for the 47-year old P. abies stand totaled
about 710 g C mÿ2 yrÿ1 (using the exponential
equation given in Table 3 with daily averages of soil
temperatures in the Of layer at 5 cm depth; data provided by C. Rebmann, Max-Planck-Institute for Biogeochemistry, Jena, Germany). Separating this ¯ux
into its microbial and root components resulted in
>500 g C mÿ2 yrÿ1 (>70%) and